1. Field of the Invention
The present invention relates to an electrophotographic apparatus using liquid toner and particularly to liquid ink or liquid toner cartridges that can be used to dispose of unused, overflow liquid ink or other unusable liquid ink or toner.
2. Background of the Art
Ink cartridges are known in the art for both ink jet and electrophotographic printing. Ink cartridges are used to introduce liquid or dry toner into a printer for use in printing and may be used for waste toner disposal as well. Some examples of combination cartridges include U.S. Pat. Nos. 6,009,289 and 6,363,233 for dry toner cartridges and U.S. Pat. No. 5,157,421 for ink jet cartridges.
An electrophotographic apparatus that uses liquid toner realizes several advantages over an electrophotographic apparatus that uses dry toner. One such advantage is the achievement of finer resolution prints due to smaller particle size. Because the particles are smaller, a lower mass of toner is required to print to the necessary optical density, reducing the cost per page. Another advantage is liquid toner's lack of airborne dry toner particulate (known carcinogens). Liquid toner also tends to have a longer shelf life because of increased charge stability with respect to dry toner.
The use of liquid toner in an electrophotographic apparatus has problems as well. For example, a typical liquid electrophotographic printer will use a hydrocarbon-based carrier liquid to transport the toner particles to the discharged area on a photoreceptor. When the ink solids have been depleted, what remains is a significant quantity of hydrocarbon solvent, possibly contaminated with charged particles and resin. Current U.S. Environmental Health Regulations will not allow hydrocarbon solvents to be disposed of in a landfill without alteration. Regulations also prohibit shipping such liquid and hazardous waste for recycling while the waste is in liquid form.
Other imaging fields can avoid these problems. In the case of dry toner, unused toner and waste toner are typically disposed of in the original cartridge and recycled by shipping the cartridge out in a mailer.
In the ink jet field, various means are employed to eliminate waste ink. Since the ink is typically aqueous, many manufacturers simply allow waste carrier to evaporate. Others realize that since the carrier is aqueous and since there is such a small quantity of waste, the cartridges may be simply landfilled. Some manufacturers include absorbents like folded paper in the cartridges to keep the waste carrier relatively immobile, as in U.S. Pat. No. 6,220,314. Some ink jet technologies, such as U.S. Pat. Nos. 5,157,421 and 6,281,911, use a two-chamber construction, with one chamber bearing fresh ink and with the waste ink being disposed of in the other chamber as it is generated. This appears to work very well for the small quantities of ink.
In the liquid electrophotographic art, these preceding solutions are not viable alternatives due to the hazardous nature of the solvent and the severe limitations placed on the shipment and disposal of the liquid.
Various means are known for removing liquid toner from a printing apparatus. Some of those means include pumping liquid from a developer unit or evaporating the used carrier from a plated image. In any case, a quantity of liquid solvent still remains, and, unless it is recycled for use in the apparatus, it cannot remain in the system. Some examples of prior art for carrier removal are U.S. Pat. Nos. 6,101,356, 6,011,943, and 5,933,689.
Most of the countries of the world maintain environmental health and safety regulations; and most of those countries do not allow liquid hazardous waste to be transported through regular delivery channels. Most of those countries also do not permit landfilling of liquid hazardous waste. As a result, liquid electrophotography has been searching for a way to safely and legally dispose of the unused and waste ink.